RFID loss-prevention using angle-of-arrival

ABSTRACT

An RFID loss-prevention system (LPS) permits authorized items to leave a facility and may perform a security action if an unauthorized item leaves the facility. A checkout reader first authorizes an item tagged with an RFID tag to exit a facility by reading an identifier from the tag, obtaining an exit authorization, and sending the identifier to a database. A reader system configured to direct at least two beams along a facility exit path reads tagged items exiting the facility, determines at least one of a travel direction and a tag location, and uses the determination to indicate that a tag is exiting or has exited the facility. The LPS then uses the database to determine if the exiting/exited tag is authorized to leave the facility.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation under 35 U.S.C. § 120 of a co-pendingU.S. patent application Ser. No. 14/925,994 filed on Oct. 29, 2015 whichis a continuation-in-part of U.S. patent application Ser. No. 14/285,534filed on May 22, 2014, now U.S. Pat. No. 9,183,717, issued on Nov. 10,2015. The disclosures of the above application are hereby incorporatedby reference for all purposes.

BACKGROUND

Radio-Frequency identification (RFID) systems typically include RFIDreaders, also known as RFID reader/writers or RFID interrogators, andRFID tags. RFID systems can be used in many ways for locating andidentifying objects to which the tags are attached. RFID systems areuseful in product-related and service-related industries for trackingobjects being processed, inventoried, or handled. In such cases, an RFIDtag is usually attached to an individual item, or to its package.

In principle, RFID techniques entail using an RFID reader to inventoryone or more RFID tags, where inventorying involves at least singulatinga tag and receiving an identifier from the singulated tag. “Singulated”is defined as a reader singling-out one tag, potentially from amongmultiple tags, for a reader-tag dialog. “Identifier” is defined as anumber identifying the tag or the item to which the tag is attached,such as a tag identifier (TID), electronic product code (EPC), etc. Thereader transmitting a Radio-Frequency (RF) wave performs theinterrogation. The RF wave is typically electromagnetic, at least in thefar field. The RF wave can also be predominantly electric or magnetic inthe near or transitional near field. The RF wave may encode one or morecommands that instruct the tags to perform one or more actions.

In typical RFID systems, an RFID reader transmits a modulated RFinventory signal (a command), receives a tag reply, and transmits an RFacknowledgement signal responsive to the tag reply. A tag that sensesthe interrogating RF wave may respond by transmitting back another RFwave. The tag either generates the transmitted back RF wave originally,or by reflecting back a portion of the interrogating RF wave in aprocess known as backscatter. Backscatter may take place in a number ofways.

The reflected-back RF wave may encode data stored in the tag, such as anumber. The response is demodulated and decoded by the reader, whichthereby identifies, counts, or otherwise interacts with the associateditem. The decoded data can denote a serial number, a price, a date, adestination, other attribute(s), any combination of attributes, and soon. Accordingly, when a reader receives tag data it can learn about theitem that hosts the tag and/or about the tag itself.

An RFID tag typically includes an antenna section, a radio section, apower-management section, and frequently a logical section, a memory, orboth. In some RFID tags the power-management section included an energystorage device such as a battery. RFID tags with an energy storagedevice are known as battery-assisted, semi-active, or active tags. OtherRFID tags can be powered solely by the RF signal they receive. Such RFIDtags do not include an energy storage device and are called passivetags. Of course, even passive tags typically include temporary energy-and data/flag-storage elements such as capacitors or inductors.

BRIEF SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended asan aid in determining the scope of the claimed subject matter.

RFID technology may be employed in loss-prevention systems used, forexample, by retailers. In one approach, a database maintains informationabout items in the store. Checkout readers authorize an item to leavethe store after a consumer pays for the item, and they provide thisauthorization information to the database. Synthesized-beam exit readersread tagged items exiting the store and check the database to determineif the item is authorized to leave.

Embodiments are directed to an RFID loss-prevention system (LPS). Acheckout reader authorizes an item tagged with an RFID tag to exit afacility by reading an identifier from the RFID tag and sending theidentifier to a database. A reader system configured to direct at leasttwo RF beams along a facility exit path reads a tagged item at an exitof the facility, determines an identifier from the tag, and determines atravel parameter for the tag. The reader system uses the traveldirection to determine whether the tag (and its associated item) isexiting the facility. The LPS accesses the database to determine if theitem is authorized to exit the facility. The LPS permits the item toexit the facility if the item is authorized or performs a securityaction if the item is not authorized.

These and other features and advantages will be apparent from a readingof the following detailed description and a review of the associateddrawings. It is to be understood that both the foregoing generaldescription and the following detailed description are explanatory onlyand are not restrictive of aspects as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The following Detailed Description proceeds with reference to theaccompanying drawings, in which:

FIG. 1 is a block diagram of components of an RFID system.

FIG. 2 is a diagram showing components of a passive RFID tag, such as atag that can be used in the system of FIG. 1.

FIG. 3 is a conceptual diagram for explaining a half-duplex mode ofcommunication between the components of the RFID system of FIG. 1.

FIG. 4 is a block diagram showing a detail of an RFID IC.

FIGS. 5A and 5B illustrate signal paths during tag-to-reader andreader-to-tag communications in the block diagram of FIG. 4.

FIG. 6 is a block diagram of a whole RFID reader system according toembodiments.

FIG. 7 is a block diagram illustrating an overall architecture of anRFID system according to embodiments.

FIG. 8 depicts an antenna array according to embodiments.

FIGS. 9A and 9B depict the antenna array of FIG. 8 synthesizing a beamin different physical directions, according to embodiments.

FIG. 10 depicts some of the potential beam locations that can besynthesized by the antenna array of FIG. 8, according to embodiments.

FIG. 11 is a diagram of a facility with a synthesized-beam reader systemconfigured for loss prevention.

FIG. 12 depicts how the angle-of-arrival of an RF wave can bedetermined.

FIG. 13 depicts several examples of how angle-of-arrival may be used todetermine the direction and/or velocity of a moving tag.

FIG. 14 is a flowchart of a loss-prevention process according toembodiments.

DETAILED DESCRIPTION

In the following detailed description, references are made to theaccompanying drawings that form a part hereof, and in which are shown byway of illustration specific embodiments or examples. These embodimentsor examples may be combined, other aspects may be utilized, andstructural changes may be made without departing from the spirit orscope of the present disclosure. The following detailed description istherefore not to be taken in a limiting sense, and the scope of thepresent invention is defined by the appended claims and theirequivalents.

As used herein, “memory” is one of ROM, RAM, SRAM, DRAM, NVM, EEPROM,FLASH, Fuse, MRAM, FRAM, and other similar information-storagetechnologies as will be known to those skilled in the art. Some portionsof memory may be writeable and some not. “Command” refers to a readerrequest for one or more tags to perform one or more actions, andincludes one or more tag instructions preceded by a command identifieror command code that identifies the command and/or the tag instructions.“Instruction” refers to a request to a tag to perform a single explicitaction (e.g., write data into memory). “Program” refers to a request toa tag to perform a set or sequence of instructions (e.g., read a valuefrom memory and, if the read value is less than a threshold then lock amemory word). “Protocol” refers to an industry standard forcommunications between a reader and a tag (and vice versa), such as theClass-1 Generation-2 UHF RFID Protocol for Communications at 860 MHz-960MHz by GS1 EPCglobal, Inc. (“Gen2 Specification”), versions 1.2.0 and2.0 of which are hereby incorporated by reference.

FIG. 1 is a diagram of the components of a typical RFID system 100,incorporating embodiments. An RFID reader 110 transmits an interrogatingRF signal 112. RFID tag 120 in the vicinity of RFID reader 110 sensesinterrogating RF signal 112 and generate signal 126 in response. RFIDreader 110 senses and interprets signal 126. The signals 112 and 126 mayinclude RF waves and/or non-propagating RF signals (e.g., reactivenear-field signals)

Reader 110 and tag 120 communicate via signals 112 and 126, which areamplitude- and/or phase-modulated waves. When communicating, eachencodes, modulates, and transmits data to the other, and each receives,demodulates, and decodes data from the other. The data can be modulatedonto, and demodulated from, RF waves, such as for signals 112 and 126.The RF waves are typically in a suitable range of frequencies, such asthose near 900 MHz, 13.56 MHz, and so on.

The communication between reader and tag uses symbols, also called RFIDsymbols. A symbol can be a delimiter, a calibration value, and so on.Symbols can be implemented for exchanging binary data, such as “0” and“1”, if that is desired. When symbols are processed by reader 110 andtag 120 they can be treated as values, numbers, and so on.

Tag 120 can be a passive tag, or an active or battery-assisted tag(i.e., a tag having its own power source). When tag 120 is a passivetag, it is powered from signal 112.

FIG. 2 is a diagram of an RFID tag 220, which may function as tag 120 ofFIG. 1. Tag 220 is drawn as a passive tag, meaning it does not have itsown power source. Much of what is described in this document, however,applies also to active and battery-assisted tags.

Tag 220 is typically (although not necessarily) formed on asubstantially planar inlay 222, which can be made in many ways known inthe art. Tag 220 includes a circuit which may be implemented as an IC224. In some embodiments IC 224 is implemented in complementarymetal-oxide semiconductor (CMOS) technology. In other embodiments IC 224may be implemented in other technologies such as bipolar junctiontransistor (BJT) technology, metal-semiconductor field-effect transistor(MESFET) technology, and others as will be well known to those skilledin the art. IC 224 is arranged on inlay 222.

Tag 220 also includes an antenna for exchanging wireless signals withits environment. The antenna is often flat and attached to inlay 222. IC224 is electrically coupled to the antenna via suitable IC contacts (notshown in FIG. 2). The term “electrically coupled” as used herein meansthat a low-impedance path exists between the electrically coupledcomponents, and may mean the presence of a direct electrical connectionor a connection that includes one or more intervening circuit blocks,elements, or devices. The “electrical” part of the term “electricallycoupled” as used in this document shall mean a coupling that is one ormore of ohmic/galvanic, capacitive, and/or inductive. Similarly, theterm “electrically isolated” as used herein means that electricalcoupling of one or more types (e.g., galvanic, capacitive, and/orinductive) is not present, at least to the extent possible. For example,elements that are electrically isolated from each other are galvanicallyisolated from each other, capacitively isolated from each other, and/orinductively isolated from each other. Of course, electrically isolatedcomponents will generally have some unavoidable stray capacitive orinductive coupling between them, but the intent of the isolation is tominimize this stray coupling to a negligible level when compared with anelectrically coupled path.

IC 224 is shown with a single antenna port, comprising two IC contactselectrically coupled to two antenna segments 226 and 228 which are shownhere forming a dipole. Many other embodiments are possible using anynumber of ports, contacts, antennas, and/or antenna segments.

Diagram 250 depicts top and side views of tag 252, formed using a strap.Tag 252 differs from tag 220 in that it includes a substantially planarstrap substrate 254 having strap contacts 256 and 258. IC 224 is mountedon strap substrate 254 such that the IC contacts on IC 224 electricallycouple to strap contacts 256 and 258 via suitable connections (notshown). Strap substrate 254 is then placed on inlay 222 such that strapcontacts 256 and 258 electrically couple to antenna segments 226 and228. Strap substrate 254 may be affixed to inlay 222 via pressing, aninterface layer, one or more adhesives, or any other suitable means.

Diagram 260 depicts a side view of an alternative way to place strapsubstrate 254 onto inlay 222. Instead of strap substrate 254's surface,including strap contacts 256/258, facing the surface of inlay 222, strapsubstrate 254 is placed with its strap contacts 256/258 facing away fromthe surface of inlay 222. Strap contacts 256/258 can then be eithercapacitively coupled to antenna segments 226/228 through strap substrate254, or conductively coupled using a through-via which may be formed bycrimping strap contacts 256/258 to antenna segments 226/228. In someembodiments the positions of strap substrate 254 and inlay 222 may bereversed, with strap substrate 254 mounted beneath strap substrate 222and strap contacts 256/258 electrically coupled to antenna segments226/228 through inlay 222. Of course, in yet other embodiments strapcontacts 256/258 may electrically couple to antenna segments 226/228through both inlay 222 and strap substrate 254.

In operation, the antenna receives a signal and communicates it to IC224, which both harvests power and responds if appropriate, based on theincoming signal and the IC's internal state. If IC 224 uses backscattermodulation then it responds by modulating the antenna's reflectance,which generates response signal 126 from signal 112 transmitted by thereader. Electrically coupling and uncoupling the antenna contacts of IC224 can modulate the antenna's reflectance, as can varying theadmittance of a shunt-connected circuit element which is coupled to theantenna contacts. Varying the impedance of a series-connected circuitelement is another means of modulating the antenna's reflectance.

In the embodiments of FIG. 2, antenna segments 226 and 228 are separatefrom IC 224. In other embodiments the antenna segments may alternativelybe formed on IC 224. Tag antennas according to embodiments may bedesigned in any form and are not limited to dipoles. For example, thetag antenna may be a patch, a slot, a loop, a coil, a horn, a spiral, amonopole, microstrip, stripline, or any other suitable antenna.

The components of the RFID system of FIG. 1 may communicate with eachother in any number of modes. One such mode is called full duplex.Another such mode is called half-duplex, and is described below.

FIG. 3 is a conceptual diagram 300 for explaining half-duplexcommunications between the components of the RFID system of FIG. 1, inthis case with tag 120 implemented as passive tag 220 of FIG. 2. Theexplanation is made with reference to a TIME axis, and also to a humanmetaphor of “talking” and “listening”. The actual technicalimplementations for “talking” and “listening” are now described.

RFID reader 110 and RFID tag 120 talk and listen to each other by takingturns. As seen on axis TIME, when reader 110 talks to tag 120 thecommunication session is designated as “R→T”, and when tag 120 talks toreader 110 the communication session is designated as “T→R”. Along theTIME axis, a sample R→T communication session occurs during a timeinterval 312, and a following sample T→R communication session occursduring a time interval 326. Of course interval 312 is typically of adifferent duration than interval 326—here the durations are shownapproximately equal only for purposes of illustration.

According to blocks 332 and 336, RFID reader 110 talks during interval312, and listens during interval 326. According to blocks 342 and 346,RFID tag 120 listens while reader 110 talks (during interval 312), andtalks while reader 110 listens (during interval 326).

In terms of actual behavior, during interval 312 reader 110 talks to tag120 as follows. According to block 352, reader 110 transmits signal 112,which is a modulated RF signal as described in FIG. 1. At the same time,according to block 362, tag 120 receives signal 112 and processes it toextract data and so on. Meanwhile, according to block 372, tag 120 doesnot backscatter with its antenna, and according to block 382, reader 110has no signal to receive from tag 120.

During interval 326, tag 120 talks to reader 110 as follows. Accordingto block 356, reader 110 transmits a Continuous Wave (CW) signal, whichcan be thought of as a carrier RF signal that is typically not amplitudemodulated or phase modulated and therefore encodes no information. ThisCW signal serves both to transfer energy to tag 120 for its own internalpower needs, and also as a carrier that tag 120 can modulate with itsbackscatter. Indeed, during interval 326, according to block 366, tag120 does not receive a signal for processing. Instead, according toblock 376, tag 120 modulates the CW emitted according to block 356 so asto generate backscatter signal 126. Concurrently, according to block386, reader 110 receives backscatter signal 126 and processes it.

FIG. 4 is a block diagram showing a detail of an RFID IC, such as IC 224in FIG. 2. Electrical circuit 424 in FIG. 4 may be formed in an IC of anRFID tag, such as tag 220 of FIG. 2. Circuit 424 has a number of maincomponents that are described in this document. Circuit 424 may have anumber of additional components from what is shown and described, ordifferent components, depending on the exact implementation.

Circuit 424 shows two IC contacts 432 and 433 suitable for coupling toantenna segments such as segments 226/228 of RFID tag 220 of FIG. 2.When two IC contacts form the signal input from and signal return to anantenna they are often referred-to as an antenna port. IC contacts 432and 433 may be made in any suitable way, such as with metallic pads andso on. In some embodiments circuit 424 uses more than two contacts,especially when tag 220 has more than one antenna port and/or more thanone antenna.

Circuit 424 includes signal-routing section 435 which may include signalwiring, signal-routing busses, receive/transmit switches, and so on thatcan route a signal to the components of circuit 424. In some embodimentsIC contacts 432/433 couple galvanically and/or inductively tosignal-routing section 435. In other embodiments (such as is shown inFIG. 4) circuit 424 includes optional capacitors 436 and/or 438 which,if present, capacitively couple IC contacts 432/433 to signal-routingsection 435. This capacitive coupling causes IC contacts 432/433 to begalvanically decoupled from signal-routing section 435 and other circuitcomponents.

Capacitive coupling (and resultant galvanic decoupling) between ICcontacts 432 and/or 433 and components of circuit 424 is desirable incertain situations. For example, in some RFID tag embodiments ICcontacts 432 and 433 may galvanically connect to terminals of a tuningloop on the tag. In this situation, capacitors 436 and/or 438galvanically decouple IC contact 432 from IC contact 433, therebypreventing the formation of a short circuit between the IC contactsthrough the tuning loop.

Capacitors 436/438 may be implemented within circuit 424 and/or partlyor completely external to circuit 424. For example, a dielectric orinsulating layer on the surface of the IC containing circuit 424 mayserve as the dielectric in capacitor 436 and/or capacitor 438. Asanother example, a dielectric or insulating layer on the surface of atag substrate (e.g., inlay 222 or strap substrate 254) may serve as thedielectric in capacitors 436/438. Metallic or conductive layerspositioned on both sides of the dielectric layer (i.e., between thedielectric layer and the IC and between the dielectric layer and the tagsubstrate) may then serve as terminals of the capacitors 436/438. Theconductive layers may include IC contacts (e.g., IC contacts 432/433),antenna segments (e.g., antenna segments 226/228), or any other suitableconductive layers.

Circuit 424 also includes a rectifier and PMU (Power Management Unit)441 that harvests energy from the RF signal received by the antenna topower the circuits of IC 424 during either or both reader-to-tag (R→T)and tag-to-reader (T→R) sessions. Rectifier and PMU 441 may beimplemented in any way known in the art.

Circuit 424 additionally includes a demodulator 442 that demodulates theRF signal received via IC contacts 432, 433. Demodulator 442 may beimplemented in any way known in the art, for example including a slicer,an amplifier, and so on.

Circuit 424 further includes a processing block 444 that receives theoutput from demodulator 442 and performs operations such as commanddecoding, memory interfacing, and so on. In addition, processing block444 may generate an output signal for transmission. Processing block 444may be implemented in any way known in the art, for example bycombinations of one or more of a processor, memory, decoder, encoder,and so on.

Circuit 424 additionally includes a modulator 446 that modulates anoutput signal generated by processing block 444. The modulated signal istransmitted by driving IC contacts 432, 433, and therefore driving theload presented by the coupled antenna segment or segments. Modulator 446may be implemented in any way known in the art, for example including aswitch, driver, amplifier, and so on.

In one embodiment, demodulator 442 and modulator 446 may be combined ina single transceiver circuit. In another embodiment modulator 446 maymodulate a signal using backscatter. In another embodiment modulator 446may include an active transmitter. In yet other embodiments demodulator442 and modulator 446 may be part of processing block 444.

Circuit 424 additionally includes a memory 450 to store data 452. Atleast a portion of memory 450 is preferably implemented as a NonvolatileMemory (NVM), which means that data 452 is retained even when circuit424 does not have power, as is frequently the case for a passive RFIDtag.

In some embodiments, particularly in those with more than one antennaport, circuit 424 may contain multiple demodulators, rectifiers, PMUs,modulators, processing blocks, and/or memories.

In terms of processing a signal, circuit 424 operates differently duringa R→T session and a T→R session. The different operations are describedbelow, in this case with circuit 424 representing an IC of an RFID tag.

FIG. 5A shows version 524-A of components of circuit 424 of FIG. 4,further modified to emphasize a signal operation during a R→T sessionduring time interval 312 of FIG. 3. Demodulator 442 demodulates an RFsignal received from IC contacts 432, 433. The demodulated signal isprovided to processing block 444 as C_IN. In one embodiment, C_IN mayinclude a received stream of symbols.

Version 524-A shows as relatively obscured those components that do notplay a part in processing a signal during a R→T session. Rectifier andPMU 441 may be active, such as for converting RF power. Modulator 446generally does not transmit during a R→T session, and typically does notinteract with the received RF signal significantly, either becauseswitching action in section 435 of FIG. 4 decouples modulator 446 fromthe RF signal, or by designing modulator 446 to have a suitableimpedance, and so on.

Although modulator 446 is typically inactive during a R→T session, itneed not be so. For example, during a R→T session modulator 446 could beadjusting its own parameters for operation in a future session, and soon.

FIG. 5B shows version 524-B of components of circuit 424 of FIG. 4,further modified to emphasize a signal operation during a T→R sessionduring time interval 326 of FIG. 3. Processing block 444 outputs asignal C_OUT. In one embodiment, C_OUT may include a stream of symbolsfor transmission. Modulator 446 then modulates C_OUT and provides it toantenna segments such as segments 226/228 of RFID tag 220 via ICcontacts 432, 433.

Version 524-B shows as relatively obscured those components that do notplay a part in processing a signal during a T→R session. Rectifier andPMU 441 may be active, such as for converting RF power. Demodulator 442generally does not receive during a T→R session, and typically does notinteract with the transmitted RF signal significantly, either becauseswitching action in section 435 of FIG. 4 decouples demodulator 442 fromthe RF signal, or by designing demodulator 442 to have a suitableimpedance, and so on.

Although demodulator 442 is typically inactive during a T→R session, itneed not be so. For example, during a T→R session demodulator 442 couldbe adjusting its own parameters for operation in a future session, andso on.

In typical embodiments, demodulator 442 and modulator 446 are operableto demodulate and modulate signals according to a protocol. A protocolis a specification or industry standard such as the Gen2 Specificationdescribed above that calls for specific manners of signaling between thereader and the tags. A protocol specifies, in part, symbol encodings,and may include a set of modulations, rates, timings, or any otherparameter associated with data communications.

In addition, a protocol can be a variant of a stated specification suchas the Gen2 Specification, for example including fewer or additionalcommands than the stated specification calls for, and so on. In suchinstances, additional commands are sometimes called custom commands. Inembodiments where circuit 424 includes multiple demodulators and/ormodulators, each may be configured to support different protocols ordifferent sets of protocols.

FIG. 6 is a block diagram of a whole RFID reader system 600 according toembodiments. System 600 includes a local block 610, and optionallyremote components 670. Local block 610 and remote components 670 can beimplemented in any number of ways. It will be recognized that reader 110of FIG. 1 is the same as local block 610, if remote components 670 arenot provided. Alternately, reader 110 can be implemented instead bysystem 600, of which only the local block 610 is shown in FIG. 1.

Local block 610 is responsible for communicating with tags. Local block610 includes a block 651 of an antenna and a driver of the antenna forcommunicating with the tags. Some readers, like that shown in localblock 610, contain a single antenna and driver. Some readers containmultiple antennas and drivers and a method to switch signals among them,including sometimes using different antennas for transmitting and forreceiving. And some readers contain multiple antennas and drivers thatcan operate simultaneously. A demodulator/decoder block 653 demodulatesand decodes backscattered waves received from the tags via antenna block651. Modulator/encoder block 654 encodes and modulates RF waves that areto be transmitted to the tags via antenna/driver block 651.

Local block 610 additionally includes an optional local processor 656.Local processor 656 may be implemented in any number of ways known inthe art. Such ways include, by way of examples and not of limitation,digital and/or analog processors such as microprocessors anddigital-signal processors (DSPs); controllers such as microcontrollers;software running in a machine such as a general purpose computer;programmable circuits such as Field Programmable Gate Arrays (FPGAs),Field-Programmable Analog Arrays (FPAAs), Programmable Logic Devices(PLDs), Application Specific Integrated Circuits (ASIC), any combinationof one or more of these; and so on. In some cases some or all of thedecoding function in block 653, the encoding function in block 654, orboth, may be performed instead by local processor 656. In some caseslocal processor 656 may implement an encryption or authorizationfunction; in some cases one or more of these functions can bedistributed among other blocks such as encoding block 654, or may beentirely incorporated in another block.

Local block 610 additionally includes an optional local memory 657.Local memory 457 may be implemented in any number of ways known in theart, including, by way of example and not of limitation, any of thememory types described above as well as any combination thereof. Localmemory 657 can be implemented separately from local processor 656, or inan IC with local processor 656, with or without other components. Localmemory 657, if provided, can store programs for local processor 656 torun, if needed.

In some embodiments, local memory 657 stores data read from tags, ordata to be written to tags, such as Electronic Product Codes (EPCs), TagIdentifiers (TIDs), keys, hashes, and other data. Local memory 657 canalso include reference data that is to be compared to the EPC,instructions and/or rules for how to encode commands for the tags, modesfor controlling antenna 651, secret keys, key pairs, and so on. In someof these embodiments, local memory 657 is provided as a database.

Some components of local block 610 typically treat the data as analog,such as the antenna/driver block 651. Other components such as localmemory 657 typically treat the data as digital. At some point there is aconversion between analog and digital. Based on where this conversionoccurs, a whole reader may be characterized as “analog” or “digital”,but most readers contain a mix of analog and digital functionality.

If remote components 670 are indeed provided, they are coupled to localblock 610 via an electronic communications network 680. Network 680 canbe a Local Area Network (LAN), a Metropolitan Area Network (MAN), a WideArea Network (WAN), a network of networks such as the internet, or amere local communication link, such as a USB, PCI, and so on. Localblock 610 may include a local network connection 659 for communicatingwith network 680. Communications on the network can be secure, such asif they are encrypted or physically protected, or insecure if they arenot encrypted or otherwise protected.

There can be one or more remote component(s) 670. If more than one, theycan be located at the same location, or in different locations. They canaccess each other and local block 610 via communications network 680, orvia other similar networks, and so on. Accordingly, remote component(s)670 can use respective remote network connections. Only one such remotenetwork connection 679 is shown, which is similar to local networkconnection 659, etc.

Remote component(s) 670 can also include a remote processor 676. Remoteprocessor 676 can be made in any way known in the art, such as wasdescribed with reference to local processor 656. Remote processor 676may also implement an encryption function, similar to local processor656.

Remote component(s) 670 can also include a remote memory 677. Remotememory 677 can be made in any way known in the art, such as wasdescribed with reference to local memory 657. Remote memory 677 mayinclude a local database, and a different database of a StandardsOrganization, such as one that can reference EPCs. Remote memory 677 mayalso contain information associated with commands, tag profiles, keys,or the like, similar to local memory 657

Of the above-described elements, it is advantageous to consider acombination of these components, designated as operational processingblock 690. Operational processing block 690 includes those componentsthat are provided of the following: local processor 656, remoteprocessor 676, local network connection 659, remote network connection679, and by extension an applicable portion of communications network680 that links remote network connection 659 with local networkconnection 679. The portion can be dynamically changeable, etc. Inaddition, operational processing block 690 can receive and decode RFwaves received via antenna driver 651, and cause antenna driver 651 totransmit RF waves according to what it has processed.

Operational processing block 690 includes either local processor 656, orremote processor 676, or both. If both are provided, remote processor676 can be made such that it operates in a way complementary with thatof local processor 656. In fact, the two can cooperate. It will beappreciated that operational processing block 690, as defined this way,is in communication with both local memory 657 and remote memory 677, ifboth are present.

Accordingly, operational processing block 690 is location agnostic, inthat its functions can be implemented either by local processor 656, byremote processor 676, or by a combination of both. Some of thesefunctions are preferably implemented by local processor 656, and some byremote processor 676. Operational processing block 690 accesses localmemory 657, or remote memory 677, or both for storing and/or retrievingdata.

RFID reader system 600 operates by operational processing block 690generating communications for RFID tags. These communications areultimately transmitted by antenna driver block 651, withmodulator/encoder block 654 encoding and modulating the information onan RF wave. Then data is received from the tags via antenna driver block651, demodulated and decoded by demodulator/decoder block 653, andprocessed by operational processing block 690.

Embodiments of an RFID reader system can be implemented as hardware,software, firmware, or any combination. It is advantageous to considersuch a system as subdivided into components or modules. A person skilledin the art will recognize that some of these components or modules canbe implemented as hardware, some as software, some as firmware, and someas a combination. An example of such a subdivision is now described,together with the RFID tag as an additional module.

FIG. 7 is a block diagram illustrating an architecture of an RFID system700 according to embodiments. For reasons of clarity, RFID system 700 issubdivided into modules or components. Each of these modules may beimplemented by itself, or in combination with others. In addition, someof them may be present more than once. Other embodiments may beequivalently subdivided into different modules. It will be recognizedthat some aspects of FIG. 7 are parallel with those describedpreviously.

RFID tag 703 is considered here as a module by itself. RFID tag 703conducts a wireless communication 706 with the remainder, via the airinterface 705. Air interface 705 is really a boundary, in that signalsor data that pass through it are not intended to be transformed from onething to another. Specifications as to how readers and tags are tocommunicate with each other, for example the Gen2 Specification, alsoproperly characterize that interface as a boundary.

RFID system 700 includes one or more reader antennas 710, and an RFfront-end module 720 for interfacing with reader antenna(s) 710. Thesecan be made as described above.

RFID system 700 also includes a signal-processing module 730. In oneembodiment, signal-processing module 730 exchanges waveforms with RFfront-end module 720, such as I and Q waveform pairs.

RFID system 700 also includes a physical-driver module 740, which isalso known as data-link module. In some embodiments physical-drivermodule 740 exchanges bits with signal-processing module 730.Physical-driver module 740 can be the stage associated with the framingof data.

RFID system 700 additionally includes a media access control module 750,which is also known as MAC layer module. In one embodiment, MAC layermodule 750 exchanges packets of bits with physical driver module 740.MAC layer module 750 can make decisions for sharing the medium ofwireless communication, which in this case is the air interface but inother embodiments could be a wired interface.

RFID system 700 moreover includes an application-programminglibrary-module 760, which can include application programming interfaces(APIs), other objects, etc.

All of these RFID system functionalities can be supported by one or moreprocessors. One of these processors can be considered a host processor.Such a host processor might include a host operating system (OS) and/orcentral processing unit (CPU), as in module 770. In some embodiments,the processor is not considered as a separate module, but one thatincludes some of the above-mentioned modules of RFID system 700.

User interface module 780 may be coupled toapplication-programming-library module 760, for accessing the APIs. Userinterface module 780 can be manual, automatic, or both. It can besupported by the host OS/CPU module 770 mentioned above, or by aseparate processor, etc.

It will be observed that the modules of RFID system 700 form a chain.Adjacent modules in the chain can be coupled by appropriateinstrumentalities for exchanging signals. These instrumentalitiesinclude conductors, buses, interfaces, and so on. Theseinstrumentalities can be local, e.g. to connect modules that arephysically close to each other, or over a network, for remotecommunication.

The chain is used in one direction for receiving RFID waveforms and inthe other for transmitting RFID waveforms. In receiving mode, readerantenna(s) 710 receives wireless waves, which are in turn processedsuccessively by the various modules in the chain. Processing canterminate in any one of the modules. In transmitting mode, waveforminitiation can be in any one of the modules. Ultimately, signals arerouted to reader antenna(s) 710 to be transmitted as wireless waves.

The architecture of RFID system 700 is presented for purposes ofexplanation, and not of limitation. Its particular, subdivision intomodules need not be followed for creating embodiments. Furthermore, thefeatures of the present disclosure can be performed either within asingle one of the modules, or by a combination of them. In someembodiments RFID system 700 can be incorporated into another electronicdevice such as a checkout terminal in a store or a consumer device suchas a mobile phone.

Everything described above in terms of readers and reader componentsfinds some correspondence with tags and tag ICs, and vice versa.Numerous details have been set forth in this description, which is to betaken as a whole, to provide a more thorough understanding of theinvention. In other instances, well-known features have not beendescribed in detail, so as to not obscure unnecessarily the invention.

In some embodiments, synthesized-beam RFID readers (SBRs) may be usedfor loss prevention. An SBR is capable of generating multiple radiofrequency (RF) beams, and may be formed by coupling one or more RFIDreaders (or distributed portions of one or more readers) to an antennaarray. FIG. 8 depicts a perspective view of an antenna array 800 withdiscrete radiating elements suitable for an SBR according toembodiments. Antenna array 800 includes an array of antenna elements 802and 804, and a ground plane 808 behind elements 802 and 804. Eachelement has a radiating direction vector 806 (only shown for oneelement) that is typically, but not necessarily, perpendicular to theground plane. An RF radiation pattern (or “beam”) for receiving ortransmitting an RF signal may be synthesized by adjusting the amplitudeand/or phase of the signals coupled from/to each antenna element 802 and804. The direction of the synthesized beam (typically represented by thedirection of the beam's primary lobe—the lobe having the highestradiated power) is controlled by these various amplitude and/or phaseadjustments. The adjustments may be analog, digital, or a mix of analogand digital. For example, during transmission, an SBR may generate theanalog signal to be transmitted, split the signal, and then direct thesplit signals to elements 802 and 804 with different amplitudes andphases. Alternatively, the SBR may synthesize different signals for eachantenna element digitally and then convert the digital signals toanalog. In other embodiments the SBR may use a mix of these approaches.Similarly, during a receive operation the SBR may combine analog signalsafter appropriate phase shifting and amplitude adjustment of each, or itmay digitize the signals from each element and combine them digitally,or a mix thereof.

The antenna elements of SBA 800 may be one or more of patch, slot, wire,horn, helical, distributed, or any other type as will be known to thoseskilled in the art. Whereas FIG. 8 only shows nine antenna elements,antenna arrays with any number of antenna elements may be used,including a single distributed element or an element made frommetamaterials. In some embodiments ground plane 808 may be nonplanar(e.g., curved, concave, convex, etc.) and in other embodiments need notexist.

FIGS. 9A and 9B show the directions of some of the RF beams that SBA900, similar to SBA 800 in FIG. 8, can generate. SBA 900 has nineantenna elements 902-918, with element 902 at the center and elements904-918 around it. The shape and direction of the beam that SBA 900generates depends on the signals to/from each element. Suppose that SBR900 transmits using primarily elements 902, 906, and 914. Then,depending on the amplitude and phase of the signals applied to theseelements, SBA 900 can steer a beam along the direction indicated bydashed line 920. In a similar fashion, suppose that SBR 900 transmitsprimarily using elements 902, 908, and 916. Then, depending on theamplitude and phase of the signals applied to these elements, SBA 900can steer a beam along the direction indicated by dashed line 922. Ofcourse, other steering arrangements are possible, including using all 9elements to transmit and/or receive in arbitrary directions and togenerate narrow beams.

FIG. 9B shows how RF beams with different directions can be synthesizedusing antenna elements located along line 920, with the diagram to theleft depicting a head-on view similar to FIG. 9A and the diagram to theright depicting a side view. As described above, the beam direction canbe controlled by varying the amplitude and phase of the signals to/fromthe antenna elements. For example, by applying a leading signal phase toelement 906, an intermediate signal phase to element 902, and a trailingsignal phase to element 914, the SBA will tend to steer its beamdownward as in beam 934. Switching leading and lagging from elements906/902 to elements 902/906 will tend to steer the beam upwards as inbeam 930. Of course, the actual beam shape depends on both the magnitudeof the phase shifting and the magnitude of the amplitude scaling (ifany).

FIG. 10 depicts potential beams from an SBR according to embodiments.Diagram 1000 depicts a side perspective of SBR 1010, capable ofsynthesizing at least five different RF beams 1012, 1013, 1014, 1015,and 1016, arranged along line 1018 (similar to line 920 in FIG. 9A),with each RF beam pointed in a different direction.

Diagrams 1020, 1040, 1060, and 1080 depict coverage areas, shown asshaded circles, of the beam patterns generated by SBR 1010. A beamgenerated by an SBR has a coverage volume, also known as the beam's“field-of-view” (FoV), which is a volume in three-dimensional spacewhere, during transmission, the transmitted energy density exceeds athreshold, and where, during receiving, the received energy densityexceeds a threshold. A beam's coverage area is a projection of thebeam's FoV on a surface. The FoV and coverage area may be differentduring transmit and receive, and may vary with reader or tag power, thethresholds, the distance between the SBR and the surface, and otherparameters.

Diagram 1020 depicts the coverage area of central beam 1012. Diagram1040 depicts the coverage areas of the inner beams such as 1014 and1015. Diagram 1060 depicts the coverage areas of the outer beams such as1015 and 1016. Finally, diagram 1080 depicts the total coverage area ofall the beams formed by SBR 1010. As shown in diagrams 1020-1080, beamcoverage areas may overlap. For example, inner beam 1014 may overlapwith the central beam 1012, with one or more other inner beams, and withone or more other outer beams.

Whereas SBR 1010 is depicted as being able to generate and switchbetween five beams on an axis (e.g., axis 1018), in other embodiments anSBR may generate and switch between more or fewer beams on any givenaxis. Similarly, whereas SBR 1010 is depicted as being able to generatebeams on four different axes (e.g., axes 920, 922, 924, and 926 in FIG.9A), in other embodiments an SBR may be configured to generate beams onmore or fewer axes. An individual beam's coverage area in FIG. 10 andsubsequent figures is depicted as circular for simplicity, and inactuality may be of any suitable shape, and may vary based oninteractions between the different elements that form the beam, as wellas the orientation and topology of the surface on which the coveragearea is projected. For example, a beam may have a non-circular coveragearea. As another example, a circular beam that illuminates a surfacewith a non-perpendicular angle may project an elliptical coverage areaon the surface.

When used to detect and inventory RFID tags, SBR 1010 may be configuredto switch between different individual beams based on a desired beamscanning timing or pattern. For example, SBR 1010 may generate a firstbeam at a first time for a first time duration, then may switch togenerating a second, different beam at a second time for a second timeduration, and so on. The order, timing, and time durations with whichSBR 1010 switches between generating different beams may be predefinedor dynamic. In one embodiment, SBR 1010 may switch between differentbeams based on a predefined schedule and scan pattern. In anotherembodiment, SBR 1010 may dynamically determine the beams to generate,the times when they should be generated, and the time durations forwhich they should be generated based on environmental or otherconditions (e.g., the actual or estimated number of tags present, actualor predicted tag movement patterns, RF interference, environmentalnoise, or any other suitable condition or parameter). In otherembodiments, SBR 1010 may generate beams by dynamically adjusting apredefined schedule and scan pattern based on environmental conditions.SBR 1010 may be configured to switch beams to optimize the number oftags inventoried, optimize the ability to detect fast-moving tags, or beconfigured to provide any desired performance metric.

FIG. 11 is a diagram 1100 of a facility 1102 with an SBR systemconfigured for loss prevention. Facility 1102 has a perimeter orboundary delimited by a physical or virtual wall, border, fence, orsimilar. Facility 1102 is depicted in FIG. 11 as a retail or wholesalestore, but in other embodiments may be a building, laboratory, yard,warehouse, distribution center, construction facility, plant, militaryinstallation, transit station (e.g., a train, bus, or subway station oran airport), ship, parking lot, shipping container, event grounds (suchas a fairground), portion or section of the above, a location within orassociated with one of the above, or similar.

Facility 1102 may include items tagged with RFID tags. A person, such asa customer, may remove an item having a tag 1104 by first obtaining exitauthorization from checkout station 1150, which includes an RFID reader.In one embodiment checkout station 1150 may be a point-of sale registeror similar checkout terminal. In another embodiment checkout station1150 may be a facility employee with a mobile checkout device such as ahandheld reader, tablet, etc. In yet another embodiment checkout station1150 may include or be a customer mobile device such as a smartphonethat has an RFID reader. Many other types and embodiments of checkoutterminals are possible. Regardless of the type, checkout station 1150reads RFID tag 1104 and authorizes it and its associated item to leavefacility 1102.

Before authorizing a tagged item to leave facility 1102, checkoutstation 1150 should obtain exit authorization, typically based onauthorizing information provided by the person (e.g. customer) or anentity/proxy acting on behalf of the person. An example of the lattermay be a facility employee, a legal authority such as a security personor the police, an autonomous entity such as a monitoring/securitysystem, or any other proxy that can act on behalf of the person. Theauthorizing information may include customer identification or accountinformation, payment, payment data (e.g., electronic currency orelectronic gift card balance), payment authorization, credit-limitinformation, proof-of-payment, or other similar information. In somesituations the authorizing information may also or instead include or bean employee number, item transportation information, a security code, alegal warrant, or other information suitable for a checkout station todetermine whether tag 1104 and its associated item are authorized toleave facility 1102.

In some embodiments checkout station 1150 can self-verify theauthorizing information and generate exit authorization. In otherembodiments checkout station 1150 will engage with a linked entity toverify the authorizing information. Examples of a linked entity includea store network, store server, payment server, bank, credit-cardcompany, legal entity such as government authority, or other networkedentity. Upon verifying the authorizing information, checkout station1150 authorizes tag 1104 and its associated item to leave facility 1102.Checkout station 1150 and/or the linked entity also informs database1160 that tag 1104 and its associated item have exit authorization.

Database 1160 stores information about tagged items associated withfacility 1102. This information may include tag identifiers; itemidentifiers; physical item information such as condition, status, orlocation; chain of custody; price; tracking information; manufacturer;any other suitable tag or item information; and/or exit authorization.Database 1160 may be accessible to checkout station 1150 via a wired(e.g., Ethernet, parallel, serial, or other suitable wired protocol) orwireless (e.g., WiFi, cellular, Bluetooth, or other suitable wirelessprotocol) connection or network. In some embodiments database 1160 maybe prepopulated with item or tag identifiers, and exit authorization isadded to the preexisting item record. In other embodiments database 1160may not contain preexisting item or tag identifiers, in which case exitauthorization causes database 1160 to generate a new item record.

In some embodiments, database 1160 is located at facility 1102, such ason a local computer, server, or RFID reader (including SBR 1110 orcheckout station 1150). In other embodiments database 1160 may belocated remotely and accessible via a network connection. Database 1160may reside on a single device (computer, server, or reader) or bedistributed among multiple devices.

Facility 1102 also includes at least one SBR 1110 positioned such thatat least some of its beams are directed along one or more exit pathspassing through exit 1120 of facility 1102. Exit 1120 may include adoor, doorway, gate, gateway, entryway, hallway, ramp, garage, elevator,escalator, stairway, stairwell, or any other suitable exit or entrance.SBR 1110 can use these particular beams, labeled as exit beams 1130, todetect RFID tags (and their associated items) near, approaching, passingthrough, or having passed through exit 1120. While SBR 1110 is locatedwithin facility 1102 in FIG. 11, in other embodiments SBR 1110 may belocated at exit 1120 or external to facility 1102, as long as at leastsome of its beams cover exit 1120 and/or exit path(s) passing throughexit 1120. SBR 1110 may be mounted so as to point downward (e.g., on theceiling of facility 1102 or in another elevated position), mounted so asto point horizontally (e.g., on a wall or other structure in facility1102), mounted so as to point upward (e.g., on, at, or under a floor orstructure in facility 1102), or some combination of the previous. SBR1110, facility 1102, database 1160, or some combination thereof may usetag reads by exit beams 1130 to determine whether a tag is exitingfacility 1102, and if so whether the tag has exit authorization, forpurposes of loss prevention. A loss-prevention system (LPS) as describedherein may include one or more of tag 1104, SBR 1110, and database 1160.In some embodiments, an LPS may also (or instead) include one or moreother, non-SBR readers (i.e., readers not configured to generatesynthesized beams). The LPS determines whether an exiting tag 1104 isfacility-owned and, if so, has exit authorization.

As an illustrative but not-limiting example, suppose that a customerpurchases an item with tag 1104 and carries the tagged item through exit1120. SBR 1110 will read tag 1104's item or tag identifier using exitbeams 1130. Upon this reading event the LPS may perform several actions.These actions may occur in series (i.e., one after the other), inparallel (i.e., two or more actions simultaneously or overlapping intime), or some combination of the two (i.e., some actions in series andsome in parallel).

A first action that the LPS may perform is to determine whether tag 1104is associated with facility 1102 (i.e., whether tag 1104 belongs to oris foreign to facility 1102). The LPS may determine the association bycomparing the tag or item identifier to a list of items known to beassociated with facility 1102. This item list is typically stored bydatabase 1160, but in some instances may be stored elsewhere such as ina networked location, in SBR 1110, or even in tag 1104. As an example ofthe latter, each tag associated with facility 1102 may include in itsmemory an owner code indicating that it is associated with facility 1102or an entity associated with facility 1102. The LPS also knows or isable to derive the owner code, and may compare the owner code read froma tag 1104 with its known owner code. As another example, the LPS may beable to derive identifiers for tags associated with facility 1102. Uponreading an identifier from a tag 1104, the LPS may compare the readidentifier to the derived identifier.

A second action that the LPS may perform is to determine whether tag1104 is passing through exit 1120. It may make this determination basedon parameters of the tag reads in exit beams 1130, such as signal phase,a received signal strength indication (RSSI), the sequence of exit beamsin which the tag is read, the identity or orientation of the exit beamsin which the tag is read, the time at which the tag was read, and/or anangle-of-arrival of one or more received tag replies. It may also, oralternatively, use or provide information such as read count per exitbeam to determine tag 1104's velocity and/or direction of travel. TheLPS may use a location-determining algorithm, a direction-determiningalgorithm, a velocity-determining algorithm, or an algorithm combininglocation, direction, and/or velocity determination to determine whethertag 1104 is passing through exit 1120. In some embodiments, the LPS mayuse one or more of the techniques described in international applicationserial number PCT/US 14/26319 filed on Mar. 13, 2014 and herebyincorporated by reference in its entirety. For example, it may use twoor more exit beams 1130 to track the movement (if any) of tag 1104 basedon a multi-session, non-acknowledging inventorying procedure asdescribed in the above-referenced international application. Finally,the LPS may determine the location of tag 1104 to confirm whether tag1104 is inside or outside facility 1102, for example using one or moretechniques described in international application serial number PCT/US14/26319 as referenced above. The LPS may determine that tag 1104 andits associated item are exiting facility 1102 if it determines that tag1104 is inside facility 1102 but approaching exit 1120, or is passingthrough exit 1120, or is outside facility 1102.

After determining tag read parameters associated with one or more tagsas described above, the LPS may store the tag read parameter(s) in adatabase (e.g., database 1160) for future reference. For example, upondetermining a tag read parameter associated with tag 1104, the LPS mayassociate the tag read parameter with an identifier of tag 1104 indatabase 1160. Subsequently, upon detecting a tag reply, the LPS may usethe stored tag read parameters to assist in identifying the replying tagand/or determining some characteristic of the replying tag (e.g.,whether the replying tag has moved, whether the tag is in an appropriatelocation, whether the tag has been authorized to exit facility 1102, orany other suitable characteristic).

As described above, facility 1102 has a boundary or perimeter that isphysical or virtual. Physical boundaries include a physical wall,border, fence, or entrance/exit through any of the previous. Virtualboundaries may be determined with respect to a physical structure (e.g.,a physical boundary such as a wall) or a location in physical space. Forexample, a virtual boundary may be defined as the perimeter or surfaceof an area or volume extending two meters outward from a wall, or may bedefined as the perimeter/surface of an area/volume extending outwardfrom a doorway in the wall.

A third action that the LPS may perform is determining whether tag 1104and its associated item are authorized to exit facility 1102. SBR 1110may communicate with database 1160, which as described above may containinformation about whether tags are authorized to exit facility 1102. Insome embodiments the LPS may determine whether a tag is authorized toexit facility 1102 based on one or more of the techniques described inU.S. Pat. No. 8,593,257 issued on Nov. 26, 2013, U.S. Pat. No. 8,866,595issued on Oct. 21, 2014, U.S. Pat. No. 8,872,636 issued on Oct. 28,2014, U.S. Pat. No. 8,866,596 issued on Oct. 21, 2014, and U.S. patentapplication Ser. No. 14/162,745 filed on Jan. 24, 2014, all of which arehereby incorporated by reference in their entireties. For example, SBR1110 may read data such as an electronic signature, a ticket, and/or anexit code from tag 1104 and the LPS may use the data to determinewhether tag 1104 and its associated item are authorized to leavefacility 1102.

As a result of the various actions described above, the LPS candetermine whether tag 1104 and its associated item belong to facility1102, are exiting facility 1102, and whether they are authorized to doso. If so authorized then the LPS permits tag 1104 and its associateditem to exit facility 1102, and may record information about the exit(e.g., time of exit, location of exit, tag and item exiting, other tagsor items exiting at the same time, etc.) in reader memory, in database1160, or in any other suitable local or remote memory. On the otherhand, if the LPS determines that tag 1104 is not authorized to exitfacility 1102 then it may take one or more security actions such assounding an audible or silent alarm, activating a security system,activating a security procedure, alerting an entity associated withfacility 1102 (e.g., an employee or manager), alerting an authority(e.g., security personnel, police personnel, military personnel, afacility supervisor, or any other authorized person), sending a messageto an entity or authority associated with facility 1102, directing acamera toward exit 1120, taking a picture or a video from a cameradirected toward exit 1120, securing a physical barrier such as locking adoor or gate or activating an obstruction (e.g., a barrier) associatedwith exit 1120, and/or any other suitable action for preventing orhindering the exit of tag 1104.

In some embodiments SBR 1110 may be used both for loss-prevention andfor inventorying tags or items in facility 1102. For example, SBR 1110may be positioned to generate exit beams 1130 directed along exitpath(s) passing through exit 1120 and at least one inventorying beam1140 directed within facility 1102. As shown in FIG. 11, inventoryingbeam 1140 may be directed to a display 1170 holding items with taggedmerchandise. In other embodiments, inventorying beams may be directed toshelves, containers, pallets, racks, counters, cases, boxes, or anyother suitable tag or item organization means. SBR 1110 may useinventorying beam 1140 to identify, locate, track, and/or authenticatetagged items within facility 1102. Upon reading a tagged item associatedwith facility 1102, SBR 1110 may update a server or database (e.g.,database 1160) with information about the tagged item, such as itslocation and/or movement.

As described above, the LPS may be configured to determine whether a tag1104 is stationary or moving. In some embodiments, the LPS may beconfigured to respond differently to a stationary tag and a tag inmotion. For example, in situations where facility 1102 contains a largenumber of tagged items, the LPS may be configured to suppress reads ofstationary tags, thereby allowing it to devote more time to readingmoving tags or other tags of interest. In some embodiments, the LPS maycause a stationary tag not to respond to one or more subsequent read ofinventorying attempts using the refresh or multi-sessionnon-acknowledging functionalities described in international applicationserial number PCT/US 14/26319 referenced above.

In some embodiments, the LPS may be configured to increase the rate atwhich moving tags are inventoried, and may be configured to maintain orreduce the rate at which stationary tags are inventoried. For example,the LPS may determine whether a tag is in motion based on beam readcounts, angle-of-arrival measurements, or any other suitable method. Insome embodiments, a tag in motion may affirmatively notify the LPS ofits movement, for example via a tag reply or by asserting a stored flag.If the LPS determines that an inventoried tag is in motion, it mayincrease the rate at which the tag is inventoried, for example bytransmitting commands specifically targeting the tag, successivelyinventorying the tag without inventorying other tags, increasing the taginventorying rates of the beams at or near the tag's location, or usingany other suitable techniques. If the LPS instead determines that aninventoried tag is stationary, it may either maintain or reduce the rateat which the tag is inventoried, for example by suppressing tag readsusing the refresh or non-acknowledging functionalities as describedabove.

In some embodiments, an LPS may determine where a tag is located and/orwhether the tag is moving based on angle-of-arrival informationassociated with responses or replies from the tag. FIG. 12 depicts howthe angle-of-arrival of an RF wave can be determined. Diagram 1200depicts a situation in which two receivers 1204 and 1206 detect an RFwave from an RFID tag 1202. Receivers 1204 and 1206 may be separatereaders, or separate antennas or antenna elements coupled to a singlereader or to multiple readers, and may be configured to each transmitdifferent beams or together synthesize a single beam oriented in aparticular direction, as described above. Receivers 1204 and 1206 andtag 1202 are disposed such that distance r₁ between tag 1202 andreceiver 1204 is greater than distance r₂ between tag 1202 and receiver1206. Accordingly, an RF wave originating from tag 1202 will firstarrive at receiver 1206 and then arrive at receiver 1204, assuming thatthe propagation paths between tag 1202 and the receivers 1204 and 1206are relatively equivalent except for distance.

The difference between the RF wave as seen at receiver 1204 and the RFwave as seen at receiver 1206 may be characterized as a time differenceor a phase difference. The former may be determined by comparing thetime at which the RF wave arrives at receiver 1204 to the time at whichthe RF wave arrives at receiver 1206. The latter may be determined bycomparing the phase of the RF wave observed at receiver 1204 at aparticular time to the phase of the RF wave observed at receiver 1206 atthe same particular time.

For example, consider RF wave 1210. At some initial time, tag 1202begins to transmit or backscatter RF wave 1210. Receiver 1206 observesthe beginning of RF wave 1210 before receiver 1204, because receiver1206 is closer to tag 1202 than receiver 1204. At some later time T,receiver 1204 then observes the beginning of RF wave 1210 as wavefront1212. At the same time T, receiver 1206 observes wavefront 1214, whichis a portion of RF wave 1210 subsequent to the wavefront 1212. Thedifference between wavefront 1212 and wavefront 1214 may be representedas a phase difference 1232, as depicted in diagram 1230. Phasedifference 1232, when combined with the (known) distance d betweenreceiver 1204 and receiver 1206, may be used to determine the angle θbetween axis 1220 on which receivers 1204 and 1206 lie and a line thatintersects both tag 1202 and the point on axis 1220 midway betweenreceivers 1204 and 1206. This angle θ may be referred to as the“angle-of-arrival” (or AoA) of RF wave 1210 with respect to thereceivers 1204 and 1206, and represents the angle from which RF wave1210 arrived, therefore may represent the angle at which tag 1202 islocated with respect to the receivers 1204 and 1206.

Instead of or in addition to using RF wave phase offsets, in someembodiments symbol offsets in a tag reply may be used to determine AoA.In some embodiments, a reply sent by tag 1202 may encode a particularsymbol sequence at a particular tag symbol rate, for example asdescribed in the Gen2 Specification. The propagation distance differencebetween tag 1202 and receivers 1204 and 1206 may cause receiver 1204 toreceive particular symbol(s) slightly after receiver 1206 receives thesame symbol(s). The timing difference in the reception of the symbol(s)may then be used to determine the AoA of the tag reply and tag 1202.

Before determining the AoA of a received tag reply, the controllercoupled to receivers 1204 and 1206 may first determine whether the tagreplies or RF waves received at receivers 1204 and 1206 are in factversions of the same signal that are phase-shifted with respect to eachother. For example, a controller may determine whether the signalsreceived at receivers 1204 and 1206 are modulated in the same way,encode the same symbols at the same tag symbol rate, or otherwiseoriginate from the same source. The controller may also determinewhether the signals received at receivers 1204 and 1206 are offset orphase-shifted with respect to each other. For example, the controllermay determine whether the two signals have a phase offset. In someembodiments, the controller may buffer at least a portion of aninitially-received tag signal and compare the buffered portion to aportion of a subsequently-received tag signal, using an appropriatephase or symbol offset if necessary. If the two portions substantiallymatch, then the controller may conclude that the initially-received andsubsequently-received tag signals correspond to the same tag signal. Ifthe controller also determines that the two signals have a phase offset,then the controller may conclude that the two signals are phase-shiftedwith respect to each other.

Using a tag signal's AoA measured with respect to a single axis (e.g.,axis 1220) localizes the tag's location to a conical surface (or acircular area if the angle-of-arrival is 90°) defined by the AoA and theaxis. Further physical constraints may further localize the taglocation. For example, receivers 1204 and 1206 may be mounted on aceiling or wall and configured to look downward or outward, which maylocalize the tag location to at most half of the conical surface definedby the AoA. Furthermore, if receivers 1204 and 1206 are mounted on aceiling and facing a floor, then the tag location may be furtherlocalized to be within some distance of the floor (or equivalently atleast some distance away from the ceiling).

In some embodiments, additional AoA measurements made using otherreceivers, may also be used to localize a tag. Diagram 1260 depictsthree noncollinear receivers 1264, 1266, and 1268. The receivers aredisposed such that receivers 1264 and 1266 lie on axis 1270, receivers1266 and 1268 lie on axis 1272, and receivers 1264 and 1268 lie on axis1274, but receivers 1264, 1266, and 1268 do not share a single axis.When a reply from tag 1262 is received, receivers 1264 and 1266 may beused to determine a first AoA θ₁ of the reply with respect to axis 1270,receivers 1266 and 1268 may be used to determine a second AoA θ₂ of thereply with respect to axis 1272, and receivers 1264 and 1268 may be usedto determine a third AoA θ₃ of the reply with respect to axis 1274. Oncetwo or more reply AoAs measured with respect to different axes areknown, triangulation may be used to further localize the location of tag1262. Using AoA measurements from three or more receivers, in additionto providing two-dimensional location capability as described above, mayallow tag location to be further refined. For example, AoA measurementsof a tag taken from three or more receivers that are not necessarilycollinear may allow the direction and/or the distance of the tag withrespect to the receivers to be determined with more accuracy, forexample by using a linear fit or some other fitting algorithm.

While angle-of-arrival determination is described above in terms ofmeasuring received signals at different receivers, in some embodimentsangle-of-arrival may be determined based on signals received ondifferent beams. A beam may be formed using a single antenna or antennaelement, or may be generated by simultaneously radiating from multipleantennas or antenna elements, as described above. In the latter case,the beam may be generated with a particular orientation and targeting aspecific location or direction, and the orientation may be used totarget tags at that specific location/direction and/or to further refinethe angle-of-arrival determination process.

FIG. 13 depicts several examples of how angle-of-arrival may be used todetermine the location, direction, and/or velocity of a moving tag.Diagram 1300 depicts a facility 1302, similar to facility 1102, with anSBR 1312 positioned to monitor facility exit 1304. SBR 1312 has multipleantenna elements, and may be configured to perform AoA measurements withits antenna elements as described in FIG. 12 to determine tag location.Initially, SBR 1312 may detect a reply from tag 1306 within facility1302 with an AoA 1322. Subsequently, SBR 1312 may detect another replyfrom tag 1306 with a different AoA 1324. SBR 1312 (or an LPS coupled toSBR 1312) may be able to use the AoAs 1322 and 1324 to determine atravel parameter associated with tag 1306. For example, as describedabove SBR 1312 may be able to determine the location of tag 1306 at aparticular time based on the measured AoAs 1322 and 1324. SBR 1312 mayalso be able to determine whether tag 1306 is stationary or moving. IfAoAs 1322 and 1324 had been substantially similar, SBR 1312 may concludethat tag 1306 is substantially stationary. On the other hand, if AoAs1322 and 1324 are substantially different, as depicted in diagram 1300,SBR 1312 may conclude that tag 1306 is moving. SBR 1312 may further beable to conclude based from the AoAs 1322 and 1324 that tag 1306 has atravel direction toward exit 1304. If timestamps associated with AoAs1322 and 1324 are available, SBR 1312 may also be able to determine anaverage travel velocity of tag 1306 in the time duration between themeasurements of AoAs 1322 and 1324.

Diagram 1330 depicts facility 1332, similar to facility 1302, with areader 1342 positioned to monitor facility exit 1334. Reader 1342 maynot be an SBR, but is configured with multiple antenna elements for AoAdetermination. Similar to the situation described in diagram 1300,reader 1332 may initially detect a reply from tag 1336 with an AoA 1352,and may subsequently detect another reply from tag 1336 with a differentAoA 1354. Reader 1332 (or an LPS or controller coupled to reader 1332)may then use the AoAs 1352 and 1354, as well as associated timestamps,to determine one or more travel parameters associated with tag 1336,such as its location, whether it is stationary or traveling, and if thelatter its direction of travel and/or velocity of travel.

Diagram 1362 depicts facility 1362, similar to facilities 1332 and 1302,with two readers 1372 and 1374 positioned to monitor facility exit 1364.Readers 1372 and 1374 are configured with multiple antenna elements forAoA determination and are depicted as similar to reader 1342, but inother embodiments, one or both of readers 1372/1374 may be SBRs similarto SBR 1312. Readers 1372 and 1374 may initially detect a reply from tag1366, with reader 1372 measuring AoA 1382 and reader 1374 measuring AoA1386. Subsequently, readers 1372 and 1374 may detect another reply fromtag 1366, with reader 1372 measuring AoA 1384 and reader 1374 measuringAoA 1388. Readers 1372 and 1374 (or an LPS/controller coupled to bothreaders) may then use the AoAs 1382-1388, as well as associatedtimestamps, to determine one or more travel parameter(s) associated withtag 1366, as described above. In some embodiments, the additional AoAmeasurements from the additional reader may be used to further refinethe travel parameter determination process.

FIG. 14 is a flowchart of a loss-prevention process 1400 according toembodiments. Process 1400 begins at step 1402, where a facility checkoutstation (e.g., checkout station 1150) reads an identifier associatedwith a tagged item. The identifier may be a tag identifier or an itemidentifier. At step 1404, the checkout station authorizes the taggeditem to leave the facility in response to receiving and verifyingauthorizing information, as described above. The checkout stationupdates a local or remote database (e.g., database 1160) at step 1406 toindicate that the tagged item is authorized to leave the facility.

Subsequently, at step 1408 one or more readers scan for tagged itemsexiting the facility using one or more beams configured to cover afacility exit or directed along exit path(s) passing through thefacility exit. The reader(s) may scan for tagged items using exit beams(for example, as described in FIG. 11) or by determiningangles-of-arrival associated with tag replies (for example, as describedin FIGS. 12-13). In some embodiments, the reader(s) may determine that atag is departing the facility based on its location, itsdirection-of-travel, and/or its velocity-of-travel. For example, if thereader(s) determines, using exit beam identifiers and/or measured AoAs,that a tag is outside the facility, then it may determine that the taghas departed the facility, especially if the tag is otherwise associatedwith the facility as described below. As another example, the reader(s)may determine that a tag with a direction-of-travel orvelocity-of-travel oriented within the facility is not departing andaccordingly ignore the incoming tag, but determine that a tag with adirection-of-travel or velocity-of-travel oriented out of the facilityis departing. The reader(s) may scan for tagged items exiting thefacility while inventorying tagged items within the facility, asdescribed above. Upon detecting a tagged item departing the facility(e.g., based on the direction-of-travel, velocity-of-travel, and/orlocation of the tag associated with the item, as described above), instep 1410 the LPS determines whether the tagged item is authorized toexit the facility. The LPS may retrieve an identifier from the tagassociated with the item and compare the identifier to a database, asdescribed above. In some embodiments, the LPS may also (or instead)retrieve an electronic signature, ticket, and/or exit code from the tagfor use in determining whether the tagged item is authorized to leavethe facility. In some embodiments, the LPS may first determine whetherthe item is associated with the facility. For example, the LPS maydetermine whether the tag identifier is included in a facility database,or whether an owner code read from the tag is properly associated withthe facility. If not, the LPS may ignore the tag and its associateditem. If the LPS determines that the item is associated with thefacility and authorized to leave the facility then the LPS permits theitem to exit at step 1412. If the LPS determines that the item isassociated with the facility but not authorized to leave then at step1414 the LPS may perform or initiate a security action as describedabove.

The steps described in process 1400 are for illustration purposes only.Loss prevention may be performed employing additional or fewer steps andin different orders using the principles described herein. Of course theorder of the steps may be modified, some steps eliminated, or othersteps added according to other embodiments.

As described above, the RF beams for transmitting and/or receiving maybe synthesized by an SBR or generated without the use of asynthesized-beam antenna. For example, a transmit beams may be generatedby a synthesized-beam antenna but the receive beam may employ a staticantenna such a patch, monopole, dipole, etc. As another example, thesynthesized beams may be replaced by multiple static antennas coupled toone or more readers.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of block diagrams and/orexamples. Insofar as such block diagrams and/or examples contain one ormore functions and/or aspects, it will be understood by those within theart that each function and/or aspect within such block diagrams orexamples may be implemented individually and/or collectively, by a widerange of hardware, software, firmware, or virtually any combinationthereof. Those skilled in the art will recognize that some aspects ofthe embodiments disclosed herein, in whole or in part, may beequivalently implemented employing integrated circuits, as one or morecomputer programs running on one or more computers (e.g., as one or moreprograms running on one or more computer systems), as one or moreprograms running on one or more processors (e.g. as one or more programsrunning on one or more microprocessors), as firmware, or as virtuallyany combination thereof, and that designing the circuitry and/or writingthe code for the software and or firmware would be well within the skillof one of skill in the art in light of this disclosure.

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its spirit and scope, as will be apparentto those skilled in the art. Functionally equivalent methods andapparatuses within the scope of the disclosure, in addition to thoseenumerated herein, will be apparent to those skilled in the art from theforegoing descriptions. Such modifications and variations are intendedto fall within the scope of the appended claims. The present disclosureis to be limited only by the terms of the appended claims, along withthe full scope of equivalents to which such claims are entitled. It isto be understood that this disclosure is not limited to particularmethods, configurations, antennas, transmission lines, and the like,which can, of course, vary. It is also to be understood that theterminology used herein is for the purpose of describing particularembodiments only, and is not intended to be limiting.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations. In addition, even if a specificnumber of an introduced claim recitation is explicitly recited, thoseskilled in the art will recognize that such recitation should beinterpreted to mean at least the recited number (e.g., the barerecitation of “two recitations,” without other modifiers, means at leasttwo recitations, or two or more recitations).

Furthermore, in those instances where a convention analogous to “atleast one of A, B, and C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, and C”would include but not be limited to systems that have A alone, B alone,C alone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). It will be further understood by those withinthe art that virtually any disjunctive word and/or phrase presenting twoor more alternative terms, whether in the description, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.”

As will be understood by one skilled in the art, for any and allpurposes, such as in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to,” “at least,” “greater than,” “less than,” and the likeinclude the number recited and refer to ranges which can be subsequentlybroken down into subranges as discussed above. Finally, as will beunderstood by one skilled in the art, a range includes each individualmember. Thus, for example, a group having 1-3 cells refers to groupshaving 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers togroups having 1, 2, 3, 4, or 5 cells, and so forth.

We claim:
 1. A method for a Radio-Frequency Identification (RFID) systemhaving first, second, and third noncollinear receivers to determine adistance to an RFID tag, the method comprising: transmitting a firstcommand; receiving in the first receiver a first tag reply, in thesecond receiver a second tag reply, and in the third receiver a thirdtag reply; determining that the first, second, and third tag replies arephase-shifted versions of a single initial reply from the RFID tagresponding to the first command; determining, from at least a firstphase difference between the first and second tag replies, a first tagread angle; determining, from at least a second phase difference betweenthe first and third tag replies, a second tag read angle; determining,from at least a third phase difference between the second and third tagreplies, a third tag read angle; and determining, from the first,second, and third tag read angles, the distance to the RFID tag.
 2. Themethod of claim 1, wherein determining the distance comprisesdetermining the distance to the RFID tag from one of the first receiver,the second receiver, the third receiver, and a combination thereof. 3.The method of claim 1, wherein determining that the first, second, andthird tag replies are phase-shifted versions of the single initial replyfrom the RFID tag comprises: determining that the first, second, andthird tag replies are versions of the single initial reply by comparingsymbols decoded from the first, second, and third tag replies; anddetermining that the first, second, and third tag replies arephase-shifted by determining a phase offset between at least two of thefirst, second, and third tag replies.
 4. The method of claim 1, furthercomprising: initially receiving a message from the RFID tag indicatingthat the RFID tag is moving; and in response, transmitting the firstcommand to specifically target the RFID tag.
 5. The method of claim 1,further comprising: transmitting a second command; receiving in a fourthreceiver a fourth tag reply, in a fifth receiver a fifth tag reply, andin a sixth receiver a sixth tag reply; determining that the fourth,fifth, and sixth tag replies are phase-shifted versions of a singlesubsequent reply from the RFID tag responding to the second command;determining, from at least a fourth phase difference between the fourthand fifth tag replies, a fourth tag read angle; determining, from atleast a fifth phase difference between the fourth and sixth tag replies,a fifth tag read angle; determining, from at least a sixth phasedifference between the fifth and sixth tag replies, a sixth tag readangle; and determining, from the distance and at least one of thefourth, fifth, and sixth tag read angles, a travel parameter of the RFIDtag, wherein the travel parameter is at least one of adirection-of-travel and a velocity-of-travel.
 6. The method of claim 5,further comprising: determining, based on the travel parameter, whetherthe RFID tag is in motion; in response to determining that the RFID tagis in motion, increasing an inventorying rate associated with the RFIDtag; and in response to determining that the RFID tag is not in motion,one of maintaining the inventorying rate and reducing the inventoryingrate.
 7. The method of claim 5, wherein at least one of the fourth,fifth, and sixth receivers is not distinct from the first, second, orthird receiver.
 8. A method for a multi-receiver Radio-FrequencyIdentification (RFID) system to locate an RFID tag, the methodcomprising: transmitting a first command; in response to transmittingthe first command, receiving first, second, and third tag replies;determining that the first, second, and third tag replies arephase-shifted versions of a single initial reply from the RFID tagresponding to the first command; determining, from at least a firstphase difference between the first and second tag replies, a first tagread angle; determining, from at least a second phase difference betweenthe first and third tag replies, a second tag read angle; determining,from at least a third phase difference between the second and third tagreplies, a third tag read angle; and determining, from the first,second, and third tag read angles, an initial location of the RFID tag.9. The method of claim 8, further comprising: initially receiving amessage from the RFID tag indicating that the RFID tag is moving; and inresponse, transmitting the first command to specifically target the RFIDtag.
 10. The method of claim 8, further comprising: transmitting asecond command; in response to transmitting the second command,receiving fourth and fifth tag replies; determining that the fourth andfifth tag replies are phase-shifted versions of a single subsequentreply from the RFID tag responding to the second command; determining,from at least a fourth phase difference between the fourth and fifth tagreplies, a fourth tag read angle; and determining, from the initiallocation of the RFID tag and the fourth tag read angle, a travelparameter of the first tag, wherein the travel parameter is at least oneof a direction-of-travel and a velocity-of-travel.
 11. The method ofclaim 10, further comprising: in response to transmitting the secondcommand, receiving fourth, fifth, and sixth tag replies; determiningthat the fourth, fifth, and sixth tag replies are phase-shifted versionsof the single subsequent reply; determining, from at least a fifth phasedifference between the fourth and sixth tag replies, a fifth tag readangle; determining, from at least a sixth phase difference between thefifth and sixth tag replies, a sixth tag read angle; and determining,from the fourth, fifth, and sixth tag read angles, a subsequent locationof the RFID tag; and wherein determining the travel parameter from theinitial location and the fourth tag read angle comprises determining thetravel parameter based on the initial location and the subsequentlocation.
 12. The method of claim 10, further comprising: determining aninitial timestamp associated with the initial reply; determining asubsequent timestamp associated with the subsequent reply; and whereindetermining the travel parameter comprises determining the travelparameter based on the initial location of the RFID tag, the fourth tagread angle, the initial timestamp, and the subsequent timestamp.
 13. Themethod of claim 10, further comprising: determining, based on the travelparameter, whether the RFID tag is in motion; in response to determiningthat the RFID tag is in motion, increasing an inventorying rateassociated with the RFID tag; and in response to determining that theRFID tag is not in motion, one of maintaining the inventorying rate andreducing the inventorying rate.
 14. The method of claim 10, furthercomprising: determining, based on the travel parameter, that the RFIDtag is leaving a facility; determining that the RFID tag is authorizedto exit the facility by at least one of: verifying at least one of anexit code associated with the RFID tag and a database entry associatedwith the RFID tag; determining that the RFID tag stores an improperowner code; and determining that the RFID tag is not present in afacility database; and in response to determining that the RFID tag isauthorized to exit the facility, allowing the RFID tag to leave thefacility.
 15. A Radio-Frequency Identification (RFID) system configuredto locate an RFID tag, the system comprising: a reader system configuredto: transmit a first command; in response to transmitting the firstcommand, receive first, second, and third tag replies; and a processormodule coupled to the reader system and configured to: determine thatthe first, second, and third tag replies are phase-shifted versions of asingle initial reply from the RFID tag responding to the first command;determine, from at least a first phase difference between the first andsecond tag replies, a first tag read angle; determine, from at least asecond phase difference between the first and third tag replies, asecond tag read angle; determine, from at least a third phase differencebetween the second and third tag replies, a third tag read angle; anddetermine, from the first, second, and third tag read angles, an initiallocation of the RFID tag.
 16. The system of claim 15, wherein the readersystem is configured to: receive the first tag reply using a firstantenna element; receive the second tag reply using a second antennaelement; and receive the third tag reply using a third antenna element,wherein the first, second, and third antenna elements are noncollinear.17. The system of claim 15, wherein the processor module is furtherconfigured to: initially receive a message from the RFID tag indicatingthat the RFID tag is moving; and in response, cause the reader system totransmit the first command to specifically target the RFID tag.
 18. Thesystem of claim 15, wherein: the reader system is further configured to:transmit a second command; and in response to transmitting the secondcommand, receive fourth, fifth, and sixth tag replies; and the processormodule is further configured to: determine that the fourth, fifth, andsixth tag replies are phase-shifted versions of a single subsequentreply from the RFID tag responding to the second command; determine,from at least a fourth phase difference between the fourth and fifth tagreplies, a fourth tag read angle; determine, from at least a fifth phasedifference between the fourth and sixth tag replies, a fifth tag readangle; determine, from at least a sixth phase difference between thefifth and sixth tag replies, a sixth tag read angle; determine, from thefourth, fifth, and sixth tag read angles, a subsequent location of theRFID tag; and determine, from the initial location and the subsequentlocation, a travel parameter of the RFID tag, wherein the travelparameter is at least one of a direction-of-travel and avelocity-of-travel.
 19. The system of claim 18, wherein the processormodule is further configured to: determine, based on the travelparameter, whether the RFID tag is in motion; in response to determiningthat the RFID tag is in motion, increase an inventorying rate associatedwith the RFID tag; and in response to determining that the RFID tag isnot in motion, one of maintain the inventorying rate and reduce theinventorying rate.
 20. The system of claim 18, wherein the processormodule is further configured to: determine, based on the travelparameter, that the RFID tag is approaching a facility exit; determinethat the RFID tag is authorized to exit the facility by at least one of:verifying at least one of an exit code associated with the RFID tag anda database entry associated with the RFID tag; determining that the RFIDtag stores an improper owner code; and determining that the RFID tag isnot present in a facility database; and in response to determining thatthe RFID tag is authorized to exit the facility, allow the RFID tag toleave the facility.